The Big Debate: Are Carbs or Fats Our Primary Fuel?

We know a few things for sure - no debate on certain critical points:

1) Both work more optimally as fuel sources when they are not mixed to any great degree in the same diet.

2) Both keto and high carb dieters report increased well being and reversal of certain diseases.

So the answer to the question which is best comes down to just that, which is best, and there are several measures that can apply:

1) Sustainability
     a. emotional - which is easier to stick with? Are we instinctually more attracted to high fat or high carb foods?
     b. nutritional - is either more likely to crash for physiologic reasons?
     c. does either introduce higher levels of toxicity?
     d. is conversion of food to fuel more efficient with either? (Ratio of calories burned to get fuel calories).

2) Longevity - does either support longer disease free life?

3) Freedom from discomfort - which feels better day to day? (Optimal health is "invisible", we are not aware of physiologic functioning until there is a problem.)
     a. Digestion is a critical function - is it "invisible"?
     b. Sleep is a critical function - is it easy and good?

4) Freedom from common diseases - are colds and allergies less likely on either?

5) When used for disease reversal
     a. which is more efficient in terms of rapidity?
     b. in terms of degree of reversal?

6) Cognitive performance - is either better?

7) Athletic performance - is either better?

8) Recovery from stressors
     a. emotional - are psychological markers better on either?
     b. physical - do high level athletes recover more quickly on either?

From everything I have seen to this point, the weight of scientific evidence (controlled trials and long term population studies) is clearly on the side of high carb. It would be interesting (but time consuming) to organize the evidence that does exist on a point by point basis.

My own anecdotal experience, what I have seen among the paleo dieters vs the high carb dieters I have had personal contact with, also leans clearly toward high carb.

The question itself, which is better, seems to have only come into clear focus recently, and further study of the specifics would clearly be helpful. Impediments to that process may be (or continue to be) the industries whose interests might be damaged by further study, including meat and dairy, pharmacology and medicine, processed food, and health care insurance.

Any of these questions could be the topic for a single blog post. I may attempt some of that going forward, meanwhile I'll let them hopefully serve simply as food for thought.